1. Field of the Invention
This invention relates to an optical source module for generating light beams having different in wavelength. Also, this invention is directed to an optical pickup apparatus for accessing a different type of optical recording media by employing the two-wavelength optical source module.
2. Description of the Prior Art
Recently, recording media require a capability of recording a high capacity of information in accordance with a trend toward a very large quantity of information. Further, optical recording media having a remarkable increase of occupation rate have been developed in the recording medium market to record a high capacity of information. Accordingly, a digital versatile or video disc (DVD), has appeared the recording capacity of which is about 6 to 7 times greater than that of the existing compact disc (CD) or rewritable compact disc (CD-R) of the write once read only memory (WROM) type. When compared with CD or CD-R, the DVD is not only higher in recording density, that is, the track density, but it is also shorter in a distance between the disc surface and the information recording face. For example, a distance between the disc surface and the information recording face is 0.6 mm in the DVD; while being 1.2 mm in the CD or CD-R. Further, the information recording faces of the DVD and the CD-R have a different reflection ratio depending upon a wavelength of light beam. Specifically, the reflection ratio in the information recording face of the CD-R has a maximum value in the case of a wavelength of 780 nm; while that of the DVD has a maximum value in the case of a wavelength of 650 nm. As described above, as optical discs with different structure and characteristics become commercially available, an optical pickup apparatus needs a capability of accessing all the different type optical discs, such as CD, CD-R and DVD. To this end, there has been suggested an optical pickup apparatus of two-beam system employing two light sources.
As shown in FIG. 1, the two-beam system optical pickup apparatus includes first and second light sources 10 and 12 installed separately to generate light beams of 650 nm and 780 nm, respectively, and a first beam splitter 14 for matching paths of the light beams from the light sources 10 and 12. When the DVD is accessed, the first light source 10 generates a light beam having a wavelength of 650 nm, hereinafter referred to as "first light beam B1", and supplies the first light beam B1, via a first collimator lens 16, to the first beam splitter 14. On the other hand, when the CD or CD-R is accessed, the second light source 12 generates a light beam having a wavelength of 780 nm, hereinafter referred to as "second light beam B2", and supplies the second light beam B2, via a second collimator lens 18, to the first beam splitter 14. For the purpose of allowing a progressive path of the first light beam B1 to be perpendicular to a progressive path of the second light beam B2, the first light source 10 is arranged in a certain horizontal position with respect to the first beam splitter 14, for example the right side in the drawing; while the second light source 12 is arranged in a certain vertical position respect to the first beam splitter 14, for example the top side in the drawing. Then, the first beam splitter 14 passes through the first light beam B1 as it is and reflects the second light beam B2 at a right angle, thereby matching the progressive path of the first light beam B1 with that of the second light beam B2. The first light beam B1 from the first beam splitter 14 is converged in a shape of spot onto an information recording face 11A of the DVD 11 by way of a second beam splitter 20, a right angle reflective glass 22 and an objective lens 24, sequentially. The light beam reflected by the information recording face 11A of the DVD 11 arrives at the surface of a multi-divisional photo detector 28 by way of the objective lens 24, the right angle reflective glass 22, the second beam splitter 20 and a sensor lens 26 in turn. Similarly, the second light beam B2 from the first beam splitter 14 is converged in a shape of spot onto an information recording face 13A of the CD or CD-R 13, via the second beam splitter 20, the right angle reflective glass 22 and the objective lens 24 in turn. Thereafter, the converged second light beam B2 is reflected by the information recording face 13A of the CD or CD-R 13 to progress toward the multi-divisional photo detector 28 by way of the objective lens 24, the right angle reflective glass 22, the second beam splitter 20 and the sensor lens 26 in turn. Then, the multi-divisional photo detector 28 converts a quantity of the light beam incident thereto from the sensor lens 26 into an electrical signal. This electrical signal includes an information recorded on the CD or CD-R 13, or the DVD 11.
As described above, however, since the two-beam system optical pickup apparatus makes use of two light sources to generate two light beams different in wavelength, it requires additional optical devices for matching the progressive paths of the light beams from the light sources. Due to this, the two-beam system optical pickup apparatus has disadvantages in that it has a complicated configuration as well as a large bulk. Further, a manufacturing process of the optical pickup apparatus becomes complicated due to the additional optical devices.